Cleanliness expectations for automatically washed dishes are often higher than those for manually washed dishes. Dishes which at first glance appear to be entirely free from food residues are then rated as not perfect if, after automatic dishwashing, stains still remain. Such stains may be based, for example, on the accretion of vegetable dyes on the dish surfaces.
Bleaching agents are conventionally used in automatic dishwashing agents in order to obtain spotless dishes. To activate these bleaching agents, and to achieve an improved bleaching action when cleaning at temperatures of 60° C. and below, automatic dishwashing agents generally also contain bleach activators. Bleach catalysts are often added to automatic dishwashing agents and have proved to be especially effective.
There are, however, limits to the use of these bleaching agents because of incompatibilities with other active washing or cleaning ingredients such as enzymes, or because of stability problems in the storage of washing and cleaning agents containing bleaching agents. This applies in particular also to liquid washing or cleaning agents.
One technical potential solution for improving the cleaning performance of automatic dishwashing agents, in particular of bleaching agent-free automatic dishwashing
One technical potential solution for improving the cleaning performance of automatic dishwashing agents, in particular of bleaching agent-free automatic dishwashing agents, includes increasing the alkalinity of these agents. For that reason the automatic dishwashing agents intended for private end consumers contain builders as a substantial constituent for both successful cleaning and rinsing. These builders firstly increase the alkalinity of the cleaning liquor since fats and oils are emulsified and saponified with increasing alkalinity, and secondly reduce the water hardness of the cleaning liquor by complexing the calcium ions contained in the aqueous liquor. Alkali phosphates have proved to be particularly effective builders, and for that reason they form the main constituent of the overwhelming majority of commercially available automatic dishwashing agents.
While phosphates are thus very highly valued in terms of their advantageous effect as a constituent of automatic dishwashing agents, their use is however not without problems from an environmental protection perspective. A substantial part of the phosphate finds its way into water bodies via domestic sewage, and in standing water bodies in particular (lakes, barrages), effectively playing a serious role in their overfertilization. As a consequence of this phenomenon, which is also known as eutrophication, the use of pentasodium triphosphate in textile washing agents has been considerably reduced through statutory regulations in many countries, for example USA, Canada, Italy, Sweden, Norway, and banned altogether in Switzerland. In Germany the maximum content of this builder in washing agents has been limited to 20% since 1984.
Along with nitrilotriacetic acid, sodium aluminum silicates (zeolites) above all are used as phosphate substitute or replacement substances in textile washing agents. For various reasons, however, these substances are not suitable for use in automatic dishwashing agents. A number of substitute substances have therefore been discussed in the literature as alternatives to alkali phosphates in automatic dishwashing agents, of which citrates should be mentioned in particular.
Phosphate-free automatic dishwashing agents which in addition to a citrate also contain carbonates, bleaching agents and enzymes are described for example in the European patents EP 662 117 B1 (Henkel KGaA) and EP 692 020 B1 (Henkel KGaA).
Another alternative to alkali phosphates, which as sole builder however is preferably used in combination with citrates, is methylglycinediacetic acid (MGDA). Automatic dishwashing agents containing MGDA are described for example in the European patent EP 906 407 B1 (Reckitt Benckiser) or in the European patent application EP 1 113 070 A2 (Reckitt Benckiser).
Despite the efforts to date, manufacturers of automatic dishwashing agents have so far not succeeded in providing phosphate-free automatic dishwashing agents that are superior or even comparable to phosphate-containing cleaning agents in terms of their cleaning and rinsing performance and particularly in terms of their deposit-inhibiting performance. Such performance parity is however a condition for the successful market launch of phosphate-free cleaning agents, as the overwhelming majority of end consumers, despite broad public debate on environmental issues, will typically decide against an ecologically advantageous product if it does not reach the market standard in terms of its price and/or performance.
A further technical possibility for improving the cleaning performance of automatic dishwashing agents consists in the use of bleaching agents. To activate these bleaching agents, and to achieve an improved bleaching action when cleaning at temperatures of 60° C. and below, automatic dishwashing agents generally also contain bleach activators or bleach catalysts, bleach catalysts in particular having proved to be especially effective.
There are however limits to the use of these bleaching agents because of incompatibilities with other active washing or cleaning ingredients such as enzymes, or because of stability problems in the storage of washing and cleaning agents containing bleaching agents. This applies in particular also to liquid washing or cleaning agents.
Accordingly, it is desirable to provide phosphate- and bleaching agent-free automatic dishwashing agents which have the characteristic feature of an improved cleaning profile in terms of typical bleach-sensitive soiling such as tea stains. Performance-improving cleaning agents and corresponding cleaning methods should therefore be made available.
This object is achieved through the addition of ethylenediamine disuccinic acid to a carbonate-containing cleaning agent formulation based on citrate. Phosphate-free automatic dishwashing agents containing ethylenediamine disuccinic acid as a complexing agent are described for example in the world patent application WO 2006/029806 A1 (BASF). Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims.